In recent years, the use of a brushless motor for a portable electric round saw has been studied for the purpose of reduction in size and weight and high efficiency. In general, the portable electric round saw has a structure including a housing with a handle on its top, a round saw driven to rotate by a motor accommodated in the housing, and a base coupled to the housing and slidable on a surface of a material to be cut. Particularly when a brushless motor is adopted as a motor, it is necessary to take measures for securing of the space to dispose a circuit board for driving the brushless motor and heat dissipation thereof.
Japanese Patent Application Laid-Open Publication No. 2010-173042 (Patent Document 1) shows an example of an electric power tool in which a brushless motor by which a polishing grind stone is driven to rotate is accommodated in a cylindrical housing grasped by a hand, and a motor driving circuit separated into a plurality of boards is accommodated at a position inside the housing on the back side of the motor opposite to a tip side of the housing at which the polishing grind stone is provided.